This variable is a flag for including local field effects when an external field is applied. The total field interacting with the molecule (also known as cavity field) is not the bare field in the solvent (the so-called Maxwell field), but it also include a contribution due to the polarization of the solvent. The latter is calculated here within the PCM framework. See [G. Gil, et al., J. Chem. Theory Comput., 2019, 15 (4), pp 2306–2319].
hamiltonian/pcm.F90 : 3228
call parse_variable(namespace, 'PCMLocalField', .false., pcm%localf)